Ka-50 Unguided Rockets Firing Possible Bug!

BitMaster · December 13, 2019

Unfortunately I havent seen one of my pals in years, he flew Cobra in Vietnam and should know this. If I can get a hold of him, I will squeeze that out of him.

The helicopter will change it's attitude, that is clear. No action goes without a counter reaction, be it thrust being deflected by some metal part of the tube or airframe, or the loss in weight, or both, I dunno, but I know it will surely not stay as it was. The faster you move the harder it gets to disturb the moving mass, so this will change with speed, I just dunno how much and if it is relevant for a specific helicopter. I could imagine that the deflected thrust might disturb the airframe, launching multiple ones then even more. Looking at thrust nozzles, those are quite small, I could imagine that.

I do know that the cobra needed FULL rudder on take-off until it had quite some forward speed, that he told me ;) Maybe worth a note.

There is another guy I know who flew choppers in Nam, the small Special Forces one, but his civ job at RAB ended and he's likely back in the US. I might get a hold of him.

* Wrote an email to my friend, I hope he is still with us. Waiting for an answer.

Edited December 13, 2019 by BitMaster

Holton181 · December 13, 2019

Seems like we agree to disagree to some extent. Fine with me. Indeed it would be good to get imput from a subject matter expert, pilot or engineer or something. Just so difficult to determine validity if just a comment from someone here at the forum claiming to be one of these.

BitMaster · December 13, 2019

Here's the answer from my fellow friend Larry, a veteran OH-6 Vietnam Pilot:

****************************************************************************

There is no change in pitch for the rockets but there is of course a weight change depending on how many you launch at one time. Most of the time you shoot in pairs but you can do many more or just salvo the load. The mini-gun will cause a change in attitude opposite the direction of target but small for the gunships. The change is a lot in the smaller OH -6 and will throw you off target if not anticipated.

The new gun ships use smart weapons so if locked on it will go find the target much easier than aiming the aircraft at the target as us older pilots did.

****************************************************************************

Holton181 · December 13, 2019

dimitriov · December 14, 2019

Hi guys,

It's a pure SAS question. Already noticed that it too happened when rocket tubes were empty and that I pushed the trigger.

The workaround is to fire with flight director engaged.

Weta43 · December 14, 2019

Hi Dimitriov -

Thanks, (but also I think that was worked out a while ago).

The question is - what is the SAS accounting for ?

OH-6 is a small aircraft, but so is the Hydra a small rocket - less than 4 kg, vs 11.4 kg for an S-8. Even firing Hydra in pairs might not produce much effect - very little weight change, very little exhaust gasses.

The fact that the Ka-50 SAS is designed to compensate for some thing (& Kamov were involved in the development of the implementation we have in DCS) means there must be something to compensate for.

I've posted videos showing both yaw and pitch from firing rockets and missiles.

The yaw must logically be a reaction against the exhaust gasses from the rocket or additional drag / lift / loss of lift from the rotor as it suddenly finds itself in a stream of gas moving at high speed in the opposite direction to the rocket.

Which is actually a culprit we haven't discussed.

David OC · December 14, 2019

Hi Dimitriov -
Thanks, (but also I think that was worked out a while ago).

The question is - what is the SAS accounting for ?

OH-6 is a small aircraft, but so is the Hydra a small rocket - less than 4 kg, vs 11.4 kg for an S-8. Even firing Hydra in pairs might not produce much effect - very little weight change, very little exhaust gasses.

The fact that the Ka-50 SAS is designed to compensate for some thing (& Kamov were involved in the development of the implementation we have in DCS) means there must be something to compensate for.

I've posted videos showing both yaw and pitch from firing rockets and missiles.

The yaw must logically be a reaction against the exhaust gasses from the rocket or additional drag / lift / loss of lift from the rotor as it suddenly finds itself in a stream of gas moving at high speed in the opposite direction to the rocket.

Which is actually a culprit we haven't discussed.

It's hard to tell if there is any real force in those video's. You can clearly see in this one there is no movement at all when firing rockets at speed from one side. I'm not saying there is no force here, it's just straight back against the round tube exiting the rear. Trying to force the nose down (pendulum) under the rotor blades.

I just find it hard that these rockets could do that against a very large moving spinning disk above.

The only thing I can think of is that these FCS systems could be needed with the larger S-13 or Vikhr missiles when Hovering or moving at very slow rate.

Vikhr missiles especially as they are generally fired when slow or hovering Plus the angle they can go to.

Weta43 · December 14, 2019

there's enough turbulence caused by the rocket motors to flame out the engine - that should rock the aircraft

David OC · December 15, 2019

Not that much I guess.

Weta43 · December 16, 2019

Not that much I guess.

Firing individual little 4kg Hydra rockets with the SAS turned on - would you expect to see anything ?

All it proves is the AH-64 SAS can compensate. (We think the Ka-50 SAS should do the same - it just isn't.)

Sure looks like a lot here

Firing a salvo of 11.5 kg S-8 from a hover @ 1:26 causes engine failure and a crash. Apparently the change in inlet pressure caused by the exhausts causes a flameout:

:book:

:yes:

There is a minimum launch speed for S-8 of 100 km/h for just that reason.

Edited December 16, 2019 by Weta43

Isegrim · December 16, 2019

Now the Apache is not the KA-50 but

After 8:50 you can see by the movement of the Gunner sight that there is something happening when the first 2 Rockets are fired. I have no idea why there is nearly nothing happening when the next 4 Rockets have been fired. Maybe another Helicopter is firing and opens the mic or the mic is open already. Also the Apaches side Cockpit Windows are made of 2mm Plexiglas and do not eat to much loud noise up.

Also keep in mind that these are firing single rounds HYDRA and not 10 or 20 S-8 rockets in a very short time wich have twice the mass.

In the KA-50 the system is for sure simply set up for the largest amount of rockets which can be fired in a single salvo, so it will overcompensate smaller salvos.

Edited December 16, 2019 by Isegrim

David OC · December 16, 2019

Firing individual little 4kg Hydra rockets with the SAS turned on - would you expect to see anything ?
All it proves is the AH-64 SAS can compensate. (We think the Ka-50 SAS should do the same - it just isn't.)

Sure looks like a lot here
Firing a salvo of 11.5 kg S-8 from a hover @ 1:26 causes engine failure and a crash. Apparently the change in inlet pressure caused by the exhausts causes a flameout:

There is a minimum launch speed for S-8 of 100 km/h for just that reason.

Yep, I was thinking it wouldn't be a good idea firing those large missile when slow IRL.:cry: They must have been testing in that vid? You think that they would have know it was a little dangerous to do.

Isegrim · December 16, 2019

Yep, I was thinking it wouldn't be a good idea firing those large missile when slow IRL.:cry: They must have been testing in that vid? You think that they would have know it was a little dangerous to do.

https://www.gazeta.ru/news/lenta/2009/07/07/n_1379762.shtml

In this report is written that they should launch the missiles out of hover so its possible its been a test.

Also is written that the exhaust gases of the rockets caused the Engine Flameout but not in detail.

Fortunately both have survived.

Weta43 · December 17, 2019

Maybe they were showing off for the press or Brass...

S.E.Bulba posted a rocket launch parameter table which showed the minimum allowable speed for launching the S-8 is something like 100 km/h, and a minimum altitude was included too.

I had also thought the problem would be the smoke being ingested (as it was for the Su-25), but Chizh posted (& maybe S.E.Bulba confirmed ?) that the issue was the high speed gasses causing turbulence, and the turbulence causing pressure changes across the intakes that caused flameouts.

Murey2 · December 17, 2019

It's funny how we started talking all about the recoil when I started this topic to talk about the weird nose jumping up (reversed recoil XD) sometimes...!

Maybe it's as BIGNEWY explained it has to do with selecting the right program! But it doesn't explain why it does that some times but not always even when it's not using the right program!?

So can we quit talking about recoil, because I have to confess I have notice recoil on some of the vids. posted here. So, this topic is about THE NOSE JUMPING UP Rapidly after shooting a salvo some times!!!!

Edited December 17, 2019 by Murey2

S.E.Bulba · December 17, 2019

Google Translate

Maybe they were showing off for the press or Brass…

Add. For reference, a few details of this incident: Kommersant ("Ъ") No.120, July 7, 2009, p.4 (in Russian).

Original in Russian

Доп. Для справки, немного подробностей данного происшествия: «Коммерсантъ» («Ъ») №120 от 7 июля 2009 года, стр.4 (на русском языке).

… I had also thought the problem would be the smoke being ingested (as it was for the Su-25), but Chizh posted (& maybe S.E.Bulba confirmed ?) that the issue was the high speed gasses causing turbulence, and the turbulence causing pressure changes across the intakes that caused flameouts.

Compressor surge (French: Pompage, Russian: Помпаж).

Turbofan Engine Malfunction Recognition and Response by B737.org.uk.

<…>

Compressor surge

It is most important to provide an understanding of compressor surge. In modern turbofan engines, compressor surge is a rare event. If a compressor surge (sometimes called a compressor stall) occurs during high power at takeoff, the flight crew will hear a very loud bang, which will be accompanied by yaw and vibration. The bang will likely be far beyond any engine noise, or other sound, the crew may have previously experienced in service.

Compressor surge has been mistaken for blown tires or a bomb in the airplane. The flight crew may be quite startled by the bang, and, in many cases, this has led to a rejected takeoff above V1. These high-speed rejected takeoffs have sometimes resulted in injuries, loss of the airplane, and even passenger fatalities.

The actual cause of the loud bang should make no difference to the flight crew's first response, which should be to maintain control of the airplane and, in particular, continue the takeoff if the event occurs after V1. Continuing the takeoff is the proper response to a tire failure occurring after V1, and history has shown that bombs are not a threat during the takeoff roll – they are generally set to detonate at altitude.

A surge from a turbofan engine is the result of instability of the engine's operating cycle. Compressor surge may be caused by engine deterioration, it may be the result of ingestion of birds or ice, or it may be the final sound from a "severe engine damage" type of failure. The operating cycle of the turbine engine consists of intake, compression, ignition, and exhaust, which occur simultaneously in different places in the engine. The part of the cycle susceptible to instability is the compression phase.

In a turbine engine, compression is accomplished aerodynamically as the air passes through the stages of the compressor, rather than by confinement, as is the case in a piston engine. The air flowing over the compressor airfoils can stall just as the air over the wing of an airplane can. When this airfoil stall occurs, the passage of air through the compressor becomes unstable and the compressor can no longer compress the incoming air. The high-pressure air behind the stall further back in the engine escapes forward through the compressor and out the inlet.

This escape is sudden, rapid and often quite audible as a loud bang similar to an explosion. Engine surge can be accompanied by visible flames forward out the inlet and rearward out the tailpipe. Instruments may show high EGT and EPR or rotor speed changes, but, in many stalls, the event is over so quickly that the instruments do not have time to respond.

Once the air from within the engine escapes, the reason (reasons) for the instability may self-correct and the compression process may re-establish itself. A single surge and recovery will occur quite rapidly, usually within fractions of a second. Depending on the reason for the cause of the compressor instability, an engine might experience:

A single self-recovering surge

Multiple surges prior to self-recovery

Multiple surges requiring pilot action in order to recover

A non-recoverable surge.

For complete, detailed procedures, flight crews must follow the appropriate checklists and emergency procedures detailed in their specific Airplane Flight Manual. In general, however, during a single self-recovering surge, the cockpit engine indications may fluctuate slightly and briefly. The flight crew may not notice the fluctuation. (Some of the more recent engines may even have fuel-flow logic that helps the engine self-recover from a surge without crew intervention. The stall may go completely unnoticed, or it may be annunciated to the crew – for information only – via EICAS messages.)

Alternatively, the engine may surge two or three times before full self-recovery. When this happens, there is likely to be cockpit engine instrumentation shifts of sufficient magnitude and duration to be noticed by the flight crew. If the engine does not recover automatically from the surge, it may surge continually until the pilot takes action to stop the process. The desired pilot action is to retard the thrust lever until the engine recovers.

The flight crew should then SLOWLY re-advance the thrust lever. Occasionally, an engine may surge only once but still not self-recover.

The actual cause for the compressor surge is often complex and may or may not result from severe engine damage. Rarely does a single compressor surge CAUSE severe engine damage, but sustained surging will eventually over-heat the turbine, as too much fuel is being provided for the volume of air that is reaching the combustor. Compressor blades may also be damaged and fail as a result of repeated violent surges; this will rapidly result in an engine which cannot run at any power setting.

Additional information is provided below regarding single recoverable surge, self-recoverable after multiple surges, surge requiring flight crew action, and non-recoverable surge. In severe cases, the noise, vibration and aerodynamic forces can be very distracting. It may be difficult for the flight crew to remember that their most important task is to fly the airplane.

Single self-recoverable surge

The flight crew hears a very loud bang or double bang. The instruments will fluctuate quickly, but, unless someone was looking at the engine gage at the time of the surge, the fluctuation might not be noticed.

For example: During the surge event, Engine Pressure Ratio (EPR) can drop from takeoff (T/O) to 1.05 in 0.2 seconds. EPR can then vary from 1.1 to 1.05 at 0.2-second intervals two or three times. The low rotor speed (N1) can drop 16% in the first 0.2 seconds, then another 15% in the next 0.3 seconds. After recovery, EPR and N1 should return to pre-surge values along the normal acceleration schedule for the engine.

Multiple surge followed by self-recovery

Depending on the cause and conditions, the engine may surge multiple times, with each bang being separated by a couple of seconds. Since each bang usually represents a surge event as described above, the flight crew may detect the "single surge" described above for two seconds, then the engine will return to 98% of the pre-surge power for a few seconds. This cycle may repeat two or three times. During the surge and recovery process, there will likely be some rise in EGT.

For example: EPR may fluctuate between 1.6 and 1.3, Exhaust Gas Temperature (EGT) may rise 5 degrees C/second, N1 may fluctuate between 103% and 95%, and fuel flow may drop 2% with no change in thrust lever position. After 10 seconds, the engine gages should return to pre-surge values.

Surge recoverable after flight crew action

When surges occur as described in the previous paragraph, but do not stop, flight crew action is required to stabilize the engine. The flight crew will notice the fluctuations described in "recoverable after two or three bangs," but the fluctuations and bangs will continue until the flight crew retards the thrust lever to idle. After the flight crew retards the thrust lever to idle, the engine parameters should decay to match thrust lever position. After the engine reaches idle, it may be re-accelerated back to power. If, upon re-advancing to high power, the engine surges again, the engine may be left at idle, or left at some intermediate power, or shutdown, according to the checklists applicable for the airplane. If the flight crew takes no action to stabilize the engine under these circumstances, the engine will continue to surge and may experience progressive secondary damage to the point where it fails completely.

Non-recoverable surge

When a compressor surge is not recoverable, there will be a single bang and the engine will decelerate to zero power as if the fuel had been chopped. This type of compressor surge can accompany a severe engine damage malfunction. It can also occur without any engine damage at all.

EPR can drop at a rate of .34/sec and EGT rise at a rate of 15 degrees C/sec, continuing for 8 seconds (peaking) after the thrust lever is pulled back to idle. N1 and N2 should decay at a rate consistent with shutting off the fuel, with fuel flow dropping to 25% of its pre-surge value in 2 seconds, tapering to 10% over the next 6 seconds.

<…>

Edited December 17, 2019 by S.E.Bulba
update.

Rogue Trooper · December 17, 2019

Hello,

This is very weird, when firing unguided rockets some times at the moment you squeeze the trigger to fire the nose of the Helicopter jump rapidly up, which make you miss the target!!

Note: This have been happening with me from long time but not always. In single Player and online. Only with unguided rockets.

In the track below you will see me firing unguided rockets twice at the first salvo firing what I described above happen and at the second that doesn't happen!?!?

Track download link below:
https://send.firefox.com/download/dcf6c377bd805513/#IQ1xhC8Wpo3QJ1Yz45pv4A

Did you try switching off the Pitch AP prior to release? I never tried this my self but I have released rockets with no APs on and this worked very well for me.

Try disengaging the pitch AP in advance so you can hold your speed and pitch with the cyclic manually.

Without doubt with AP on or off, I always race into the target in order to maintain high speed so that I can defensively manoeuvre if something dangerous appears when I least expect it. I always need to pitch up to attain the perfect target when it is time to release the unguided rockets..... and I always adjust when it is time to fire.... could this be something?

IS there a lack of collective control when the time of release has suddenly come?

Edited December 18, 2019 by Rogue Trooper

Ka-50 Unguided Rockets Firing Possible Bug!

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